How to resize selected part of uv image in python?
At last, i've found an answer:

#edit the object
bpy.ops.transform.resize(value=(0.1, 0.1, 0.1))
#edit the image's selected part size
bpy.ops.uv.smart_project(island_margin=0.4)
#come object to first status
bpy.ops.transform.resize(value=(10, 10, 10))


I know, it's a kludge. But it's a pretty kludge, and works! :)

Thanks everybody.